EP0212090B1 - Doppler blood velocimeter with range continuity - Google Patents

Doppler blood velocimeter with range continuity Download PDF

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Publication number
EP0212090B1
EP0212090B1 EP86107241A EP86107241A EP0212090B1 EP 0212090 B1 EP0212090 B1 EP 0212090B1 EP 86107241 A EP86107241 A EP 86107241A EP 86107241 A EP86107241 A EP 86107241A EP 0212090 B1 EP0212090 B1 EP 0212090B1
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EP
European Patent Office
Prior art keywords
range gate
signal
doppler
unaliased
range
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Expired - Lifetime
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EP86107241A
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German (de)
English (en)
French (fr)
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EP0212090A1 (en
Inventor
Philip A. Desjardins
Jeffry E. Powers
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Advanced Technology Laboratories Inc
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Advanced Technology Laboratories Inc
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Priority to AT86107241T priority Critical patent/ATE59764T1/de
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/06—Measuring blood flow

Definitions

  • the present invention relates to an improved medical ultrasound Doppler unit of the type used for measuring velocity of blood flow.
  • the invention relates to a pulsed Doppler ultrasound velocimeter and to an anti-aliasing method for use with multigate Doppler means.
  • Pulsed Doppler velocimeters can discern only a limited range of Doppler-shifted frequencies. This limitation arises from insufficient time-sampling of the Doppler signal. Pulsed Doppler velocimeters sample a Doppler-shifted signal at a single arbitrary depth, a depth determined by the delay between the insonifying pulse and the sampling time. This sampling, performed at a rate called the Pulsed Repetition Frequency (PRF) limits the maximum unambiguously discernable Doppler-shifted frequency, and, therefore, the maximum discernable velocity.
  • PRF Pulsed Repetition Frequency
  • the Nyquist Sampling Theorem implies that a pulsed Doppler velocimeter can unambiguously discern only those Doppler-shifted frequencies which are between -PRF/2 and +PRF/2. Any Doppler-shifted frequency outside of this interval (hereafter called the "Nyquist interval”) will be aliased, that is, it will appear to be at a frequency that is inside this interval. Without additional information, the pulsed Doppler velocimeter cannot discern whether a perceived Doppler-shifted frequency is actually within the Nyquist interval or whether it is an alias of a frequency outside of this interval.
  • ROUND(X) is a function which rounds the number inside the parentheses, i.e., ROUND(X) will be an integer which is equal to the greatest integer in X, plus 1 if the remaining fractional part is greater than or equal to 0.5.
  • the perceived frequency is always within the Nyquist interval. If the true frequency is also between -PRF/2 and PRF/2, then no aliasing occurs, and the perceived frequency is the true frequency. If the true frequency is outside the Nyquist interval, then the true frequency appears to be the perceived frequency as found in (eq. 2).
  • the ROUND function in the above equation can alias several possible true frequencies (f t 's) onto the same perceived frequency fp. Accordingly, there is no direct way to determine whether the perceived frequency is the true frequency or one of many possible aliases.
  • Another approach is to deccrease the transmitted frequency in order to proportionally decrease the Doppler-shifted frequency.
  • a disadvantage of this common technique is the problem of decreased scattering and decreased spatial resolution.
  • the signal from a desired range cell of depth, d is sampled by delaying the sample with respect to the insonifying pulse by a time, t, found by:
  • Equation 3 does not separate the desired range's signal from signals coming from deeper ranges (which were insonified by prior pulses). That is, it also receives signals from ranges at the following depths:
  • n is an integer which is greater than or equal to 1.
  • WO-Al-85/02105 discloses a Doppler ultrasound apparatus for providing two-dimensional blood flow data.
  • the 'probe includes an array of transducers that produce an ultrasound beam that can be electrically scanned over a sector. For each angle scanned, a burst of energy is transmitted and the energy reflected by the blood is periodically .sampled by range gates. As a result, blood flow data at a plurality of points along a plurality of scan lines are produced.
  • the sampling frequency or pulse repetition rate should be at least twice the frequency of the maximum Doppler shift produced by the blood. As a result, aliasing will not occur and data will not be erroneously interpreted.
  • the range of the system is limited because signals reflected by blood distant from the transducers are unable to make it back to the array before the next pulse is transmitted.
  • the baseline estimate, f(i) is periodically updated in order to track non-stationary Doppler spectra (such as caused by the variation of blood velocity distribution over the cardiac cycle, as seen by Doppler blood velocimeters).
  • a second disadvantage of this method is that the technique assumes that the time between frequency estimates is sufficiently short such that the difference between the true frequencies f t (j) and f t (i) is within the Nyquist interval. If the Doppler spectrum changes sufficiently between updates, then future estimates will be corrupted.
  • Range-continuity anti-aliasing corrects for aliasing by first making a frequency estimate, f(i), at an arbitrary range cell r(i). Any perceived frequency fp(j) estimated at a nearby range cell r(j) is compared to f(i) and corrected for aliasing according to equation 5. The most likely frequency, f ml (j), at range cell r(j) is found by:
  • r(j) and f m ,(j) become the new r(i) and f(i), respectively, and a new range is chosen as r(j).
  • This technique assumes that the original f(i), called f(0), is correct to within ⁇ PRF/2. This can be done by choosing a range r(0) where it is assumed there are no moving targets. The frequency f(0) estimated at this range is assumed to be within the Nyquist interval and is set to fp(O).
  • the correction circuitry assumes that the signal is noise and sets the most-likely frequency to be the perceived frequency.
  • This technique requires the ability to simultaneously acquire Doppler-shifted signals from multiple range cells. Accordingly, the use of this technique requires a "multigate Doppler".
  • This technique requires a frequency estimator that operates at any or all the acquired range cells. This frequency estimator calculates the perceived frequency fp, a frequency which is within the Nyquist interval.
  • the disclosed technique assumes that the true Doppler-shifted frequency varies slowly in range.
  • the distance between r(i) and r(j) must be sufficiently short such that the difference between the true frequencies, f,(i) and f,(j), is within ⁇ PRF/2. This means there must be sufficient spatial sampling in range.
  • the invention 10 is comprised of a multigate Doppler unit 12.
  • the term "multigate Doppler unit” refers to an apparatus which may be used to acquire Doppler signals at multiple depth ranges. Devices of this type have been used heretofore and are considered, forthe purposes of this invention, to be well known to those of ordinary skill in the art.
  • the outputs of the multigate Doppler unit 12 consist of Doppler signals at various depth ranges. Thus, an output signal at range i appears on a first line 14, and an output signal range j on a second line 16. These output siganls, are (i) and (j), respectively. These output signals go into frequency estimators 18, 20.
  • a frequency estimator is a device capable of estimating frequency of the Doppler signal.
  • the output of each of the frequency estimators 18, 20 is the perceived frequency fp(i) and fp(j), respectively and will be in the range of ⁇ PRF/2. As discussed above, the perceived frequency may be aliased. Accordingly, the perceived frequency outputs of the frequency estimators 18, 20 are fed into frequency corrector circuits 22, 24.
  • the job of the frequency corrector circuits 22, 24 is to correct the perceived frequency, fp, by adding the proper multiple of the PRF which is found by using equation 6.
  • the proper multiple will be an integer which is found iteratively.
  • the assumption is made that the velocity in the selected depth range will not vary significantly from the velocity of the preceding depth range. This means that if the output of corrector 22 is f m ,(i) then the output of corrector 24 will be fp(j) plus a multiple of PRF found by rounding the difference between f m ,(i) and fp(j) to the integer corresponding to the nearest multiple of PRF.
  • each output frequency will be correct if two assumptions are correct.
  • the blood flow must be within the sample depth and has not changed significantly from the blood flow in the adjacent sample depth, i.e., the Doppler signal is within ⁇ PRF/2 of the Doppler signal of the adjacent sample depth.
  • the present invention assumes that there is no movement in the shallowest range and the initial most likely frequency, f m ,(0) of the first corrector 22 is set to fp(O) on line 26. Thereafter, f m ,(i) on line 28 is used as the correcting frequency which is input into the corrector 24 to compute f m ,(j).
  • the corrector assumes that there is no blood flow at the corrector depth and f ml out of that corrector will be set to fp.
  • the preferred embodiment 100 of the present invention is shown.
  • a multigate Doppler unit 102 which generates time-multiplexed samples of the Doppler sent via output line 104 into a frequency estimator 106.
  • the multigate Doppler unit 102 may start with the most shallow depth and then step deeper into successive sample groups from adjacent sample depths to provdie a frequency estimator 106 with Doppler signals.
  • the output of the frequency estimator 106 will be a perceived frequency fp(k) for each depth k.
  • That perceived frequency fp(k) is set into a corrector circuit 110 via line 108, and output of the corrector circuit 110 will be the most likely frequency depth k, f ml (k) on line 112.
  • f ml (k) is also set into a delay unit 114 which samples the f m ,(k) and holds it while the multigate Doppler unit 102 steps into the next depth. Accordingly, the output of the delay unit 114 will be the most likely frequency at depth k-1 on line 116.
  • the assumption is made that at depth 0 there is no blood flow. Accordingly, the frequency f ml (0) is initialized to fp(O), and subsequent depths are adjusted to provide the most likely frequency thereafter.

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  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Heart & Thoracic Surgery (AREA)
  • Medical Informatics (AREA)
  • Biophysics (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Pathology (AREA)
  • Radiology & Medical Imaging (AREA)
  • Engineering & Computer Science (AREA)
  • Biomedical Technology (AREA)
  • Hematology (AREA)
  • Physics & Mathematics (AREA)
  • Molecular Biology (AREA)
  • Surgery (AREA)
  • Animal Behavior & Ethology (AREA)
  • General Health & Medical Sciences (AREA)
  • Public Health (AREA)
  • Veterinary Medicine (AREA)
  • Ultra Sonic Daignosis Equipment (AREA)
  • Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)
  • Investigating Or Analysing Biological Materials (AREA)
  • Measuring Pulse, Heart Rate, Blood Pressure Or Blood Flow (AREA)
EP86107241A 1985-05-30 1986-05-28 Doppler blood velocimeter with range continuity Expired - Lifetime EP0212090B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT86107241T ATE59764T1 (de) 1985-05-30 1986-05-28 Doppler-blutgeschwindigkeitsmesser mit bereichsstetigkeit.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US73925485A 1985-05-30 1985-05-30
US739254 1985-05-30

Publications (2)

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EP0212090A1 EP0212090A1 (en) 1987-03-04
EP0212090B1 true EP0212090B1 (en) 1991-01-09

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EP86107241A Expired - Lifetime EP0212090B1 (en) 1985-05-30 1986-05-28 Doppler blood velocimeter with range continuity

Country Status (5)

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EP (1) EP0212090B1 (ja)
JP (1) JPH0685777B2 (ja)
AT (1) ATE59764T1 (ja)
CA (1) CA1262276A (ja)
DE (1) DE3676755D1 (ja)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0685778B2 (ja) * 1987-03-06 1994-11-02 アロカ株式会社 超音波診断装置
JPH0213441A (ja) * 1988-06-30 1990-01-17 Yokogawa Medical Syst Ltd 超音波パルスドプラ装置
WO1991015780A1 (en) * 1990-03-30 1991-10-17 Shigeo Ohtsuki Method of processing doppler signal
FR2712700B1 (fr) * 1993-11-18 1996-02-02 Rhea Acquisition et validation des mesures de vitesse de corde d'un écoulement hydraulique en collecteur d'assainissement.
DE112008000493A5 (de) * 2007-02-21 2010-02-11 Universität Duisburg-Essen Verfahren und Vorrichtung zur Ultraschall-Messung von Blutfluß

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2323366B1 (fr) * 1975-09-15 1978-09-01 Inst Nat Sante Rech Med Procede et dispositif de visualisation vasculaire par ultra-sons
US4217909A (en) * 1978-08-23 1980-08-19 General Electric Company Directional detection of blood velocities in an ultrasound system
FR2506472B1 (fr) * 1981-05-25 1985-06-21 Inst Nat Sante Rech Med Procede et appareil de mesure en temps reel pour la visualisation des vitesses d'ecoulement dans un segment de vaisseau
JPS6055934A (ja) * 1983-09-08 1985-04-01 松下電器産業株式会社 超音波血流計
JPS62500283A (ja) * 1983-11-10 1987-02-05 アク−ステツク　パ−トナ−ズ　ア　リミテツド　パ−トナ−シツプ 超音波診断装置

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Publication number Publication date
CA1262276C (en) 1989-10-10
JPH0685777B2 (ja) 1994-11-02
DE3676755D1 (de) 1991-02-14
EP0212090A1 (en) 1987-03-04
CA1262276A (en) 1989-10-10
ATE59764T1 (de) 1991-01-15
JPS61279233A (ja) 1986-12-10

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